1. Field of the Invention
The present invention relates generally to a lens controller, and more particularly to a lens controller which generates control signals for controlling a broadcast zoom lens used for a studio camera, a field camera, and the like.
2. Description of Related Art
Zoom speed controlling is usually performed in order to control the zooming of a large-sized lens by a servo-control for a studio camera and a field camera. A user performs the zooming operation by rotating a thumb ring of a zoom controller, which is attached to a grip of a pan/tilt handle. The zoom controller determines the rotational angle of the thumb ring by a potentiometer, and the direction in which the thumb ring is rotated from a neutral position determines the tele direction or the wide direction. The motor of the zoom lens is controlled so that as the rotational angle of the thumb ring increases, the zoom speed increases.
In a conventional zoom controller, however, the zoom controller must deal with a wide dynamic range (a wide variable range of the zoom speed) of which zoom speed ranges from a maximum speed for moving the lens over the whole movable range in a fraction of a second to a minimum speed for moving the lens over the whole movable range in several hundred seconds (e.g. 200 seconds). For this reason, the zooming must start when the control signal is several millivolts (mV). Thus, there is a problem in that the undesired zooming operation can occur due to small errors (displacement) and changes of the control signal, which are caused by the mechanical displacement of the potentiometer of the zoom controller, secular changes of the mechanical system in the zoom controller, drift of parts of the zoom controller, noise from the outside, and the like.